The most common type of roof construction in use today involves a slanted roof positioned over a building such as a house which roof extends beyond the edges of the building to form eaves and rake projections. In the winter heat rises from within the house and melts snow on the top surface. The water therefrom runs down the slanted roof to the eave portion which is not heated and refreezes forming ice dams that are dangerously heavy and destructive to the structure. In addition, the dams back up water under the shingles causing leaks and deterioration.
In the prior art this problem has been approached by attempting to insulate the roof covering better. However, this approach can never be fully successful because no matter how much insulation is utilized the internal heat eventually leaks through by conduction to the outside surface during the course of the winter and creates melting conditions. It is necessary that an absolutely cold roof surface be created and maintained irrespective of the heat flow from inside the building.
One prior art approach described in U.S. Pat. No. 4,023,321 employs shingles having tiny air passages formed in the shingle to allow ventilating air from the outside to isolate the top surface of the shingle. However, these air passages are so small that not much air can be expected to pass through and they are soon clogged with dirt and moisture. In addition, the shingle actually has more solid area than ventilating area and thus the heat can still conduct through in the spaces between and beside the tiny air passages. Also, since the entrance and exit ends of the ventilating passageways are at the same height there can be no draft effect to encourage the passage of air. My invention overcomes these problems.